Taxonomic revision of the biotechnologically important species Penicillium oxalicum with the description of two new species from acidic and saline soils

Penicillium oxalicum is a frequently isolated fungus exhibiting a wide range of physiological activities that are of relevance in agriculture, biotechnology, food quality assessments, and medicine. Although widely studied, this fungus is usually identified on the basis of morphological characters but its taxonomy has never been systematically revised. In this study, we revised a set of Penicillium isolates from various sources including P. oxalicum-like strains obtained from acidic and saline soils in the Soos Nature Reserve (Czech Republic). Two phylogenetic sister species of Penicillium oxalicum are illustrated and described as Penicillium diatomitis sp. nov. (CCF 3904T) and Penicillium soosanum sp. nov. (CCF 3778T). Both species can be distinguished from P. oxalicum based on molecular data, morphological characters, and extrolite profiles. Penicillium diatomitis mimics P. oxalicum by its macro- and micromorphology but acid production on CREA distinguishes between the two.